The general opinion is that the era of the great rigid airships (Zeppelin) has passed. This is primarily because of the Lakehurst disaster (May 6, 1937), when the airship LZ 129, filled with hydrogen as its buoyant gas, burnt out, and the fact that today's aircrafts are about ten times faster than airships and 20 times faster than ships. Consequently, practically all long-distance passenger traffic is now the realm of aircraft.
The state of the art in airship construction has virtually rested since the end of large airship building in about 1940. The prototypes of all following airships were the last Zeppelins LZ 129 and LZ 130. Although designs for unusual airships were published, in toroidal form for instance (eg DE-OS 28 14 309), they were never actually implemented because of the unsuitability of the structure (eg polyethylene skin for a torus of 400 m in diameter).
For the large airships that emerged since then, the three major problems were as follows:
1. high sensitivity to cross winds because of the form and fins, PA1 2. flying without ballast and/or gas loss, and PA1 3. landing and anchoring.
Ejecting ballast and releasing gas were indispensable in conventional airships. When the airship started, ballast (usually water) was first ejected to allow a sufficiently fast climb to a height of 50 to 100 m, where the propulsion engines were started to bring the airship to its cruising altitude at an angle of climb of about 10.degree. by dynamic lift. As a result of decreasing air pressure with increasing altitude, the buoyant gas in the gas cells expands and thus produces the lift, until it is lowered by releasing gas at the required altitude in order to keep equilibrium with the weight of the airship so that the latter can continue to travel in the normal horizontal position with the least resistance (at 10.degree. angle of incidence the aerodynamic resistance of ellipsoids increases by about a third). Accordingly, the airship has too great a lift for descent and generally cannot descend fast enough only through dynamic downward drift and a negative angle of incidence, so all that remains is to release gas.
Fuel consumption was another difficulty, in that the fuel in the engines of the airships combusted into gaseous products that escaped into the atmosphere creating lift corresponding to the weight of the combusted fuel, which to begin with could only be compensated by releasing buoyant gas. For consumption of 80 t per trip for example, this meant a loss of about 70,000 m.sup.3 of buoyant gas through releasing it. Gas loss of this order would be financially unsupportable in the case of the helium that is now prescribed as the buoyant gas.
In LZ 130 this problem was solved by conducting the exhaust gases of the engines through a cooling system in which the water of combustion condensed and entered into the ballast water tanks to compensate quite precisely the weight lost through fuel consumption. However, the cooling system meant extra weight of 4 t and extra fuel consumption of 2 t for a 100 hour trip, with the result that the payload reduced by 6 t.
As another way of avoiding helium losses, DE-OS 28 14 309 mentions the liquefaction of buoyant gas by a gas liquefying plant borne in the airship to aid the descent of a toroidal airship. But this system is bound to the size relations of the airship, which are practically impossible to implement.
Helium, the only practicable buoyant gas for manned airships, is the most difficult gas to liquefy. The only practical solution for large volumes of gas is compression followed by cooling (with the aid of liquid nitrogen) and decompression with external work output. Using this process the Linde-Kryotechnik firm (Winterthur) has implemented systems (drive power of 1850 kW) with capacity of 2400 l of liquid helium per hour. The production of one liter of liquid helium takes about 1 kWh, the consumption of liquid nitrogen in the process already being considered. With these figures one can calculate that, to compensate 80 t weight loss through fuel consumption for example, some 62,000 m.sup.3 of helium gas would have to be liquefied. This means, however, that through the power consumption of the system, extra fuel consumption of some 12.5 t results, which in turn would have to be compensated by further liquefaction of helium, while the system for recovery of combustion water would only have extra fuel consumption of 2.5 t, which furthermore compensates itself. So the use of a large helium liquefying plant solely for the purpose of compensating weight loss through fuel consumption is meaningless.
A further problem is that of anchoring airships during and after landing. A common procedure is to throw manropes from the airship to a multi-man team that then pulls the airship to its anchorage and moors it to posts in the ground. Subsequently, for protection against the weather and storms, the airship is towed by a vehicle or the anchor team from where it has moored into a large hangar. Another method is what is called mooring on a high mast, where a locking device in the nose of the airship engages with a matching counterpart on the rotatable tip of a mast about 50 m in height for example. Passengers, crew and freight reach the mast through a walkway and then descend to the ground by an elevator. Both of these procedures are detailed by P. Kleinheins (publisher) in "Die grossen Zeppeline" (Dutsseldorf, VDI-Verlag, 1996).
These procedures cost material, personnel and time. If the appropriate installations do not exist, landing is dangerous and difficult. That is one of the major reasons why airship travel to date, especially by large rigid airships, which is the only category that comes into question for transporting passengers on a large scale, has been so uneconomical, in other words why it has played no role for the past 50 years.
Smaller nonrigid dirigibles (blimps) are also known, for which improvements have been published, eg for magnetic mooring (U.S. Pat. No. 4,238,095 and U.S. Pat. No. 4,272,042) or for liquefaction of the buoyant gas in a gas liquefying plant onboard an extremely large airship to generate downward drift (DE-OS 28 14 309). However, these developments, because of the difference in sizes, are not suitable as stimulus for further developments where large airships are concerned.
In particular, the described landing procedures and installations cannot be scaled to airships with large numbers of passengers (eg some 350) and matched to today's safety regulations for transportation of persons. This also applies to the landing procedure in the above mentioned US patent, which, because of the permanent magnets that are used, is only suitable for small nonrigid dirigibles. An electromagnet on the rubber skin of the nonrigid dirigible is only suggested for mast mooring, this magnet being very low in weight and thus having little magnetic force.
Thus, it would be advantageous to provide an improved rigid airship that exhibits less sensitivity to side winds, with which a large number of passengers can be transported for reduced energy consumption per passenger, and that demonstrates improved maneuverability.